An electric vehicle (EV) of a mass production first generation is equipped with a motor as an alternative of an internal combustion engine, and a single motor is provided for a vehicle. In a future EV/hybrid electric vehicle (HEV) with a higher price range, it is considered that vehicles equipped with a plurality of motors increase to make a difference.
Front and rear twin motor-mounted vehicles having a front wheel motor and a rear wheel motor have a four-wheel drive system in view of the configuration, and the starting and acceleration performances are improved. Since the kinetic energy during deceleration can be regenerated by the front and rear wheels even during turning, it is easy to increase the amount of regeneration. Particularly, by distributing the regenerative torque depending on the load, it is possible to maximize the amount of regeneration (it is possible to perform deceleration/regeneration in a stable posture like the front and rear distribution of brake torque).
In contrast, in the left-right twin motor arrangement, at the time of turning, kinetic energy is regenerated in the inner wheel to obtain the deceleration force and electric energy, and acceleration force is obtained by operating the outer wheel using this energy, thereby performing a direct yaw-moment control (DYC). However, since the turning speed of the inner wheel is lower than that of the outer wheel, the inner wheel can generate power only at a lower voltage than the counter electromotive voltage of the outer wheel side. Therefore, although the regenerative power generation is possible in the inner wheel, substantially, electric energy is taken out of the battery and is supplied to the outer wheel side, and the whole vehicle can hardly regenerate the kinetic energy at the time of turning.
Also, although the front and rear twin motor-mounted vehicles are driven by all wheels, in the case of the left and right twin motor arrangement, another motor is required for driving all the wheels, which leads to increases in cost and weight. In this way, the merit of the right and left twin motor arrangement is the elimination of the differential gear and the possibility of DYC. However, in DYC, a roll moment is generated from an imbalance between the left and right link half forces generated by the braking force/driving force, and in many cases, natural coupling of the yaw motion and the roll motion is often impaired.
Based on the aforementioned background, it is desirable to obtain turning performance equal to or higher than that of the left and right twin motor-mounted vehicles by finding the front-rear distribution control contents that improve the turning performance (maneuverability and stability) of the front and rear twin motor-mounted vehicles. Further, a method of dynamically controlling the front-rear distribution ratio is also applicable to vehicles having the front-rear distribution function among conventional four-wheel drive vehicles that achieve four-wheel drive with one prime mover as well as the EV/HEV.
In order to solve this problem, for example, PTL 1 discloses a technique of a driving force distribution total control system of front-rear wheels and left-right wheels which includes a front and rear wheel driving force distribution control system which controls distribution of driving force to front and rear wheels according to a predetermined vehicle state, a left and right wheel driving force distribution control system which controls the driving force distribution to left and right wheels according to a predetermined vehicle state, an oversteering moment detecting means for detecting the time when an oversteering moment occurs or is predicted to occur by control on the left and right wheel driving force distribution control system side at the time of turning, and a first total control means for performing a correction control in which a front wheel distribution amount corresponding to the amount of oversteering moment detection is added at the time of detection of an oversteering moment on the front and rear wheel driving force distribution control system side. Further, PTL 1 discloses a technique of a driving force distribution total control device of front-rear wheels and left-right wheels which includes an understeering moment detecting means for detecting the time when an understeering moment occurs or is predicted to occur by the control of the front and rear wheel driving force distribution control system side at the time of turning, and a second total control means for performing a correction control in which the turning outer wheel distribution amount corresponding to the amount of understeering moment detection is added at the time of detection of the understeering moment on the left-right wheel driving force distribution system side.
Further, PTL 2 discloses a motion control method of a vehicle in which an input lateral jerk (Gy_dot) of a vehicle is multiplied by a prestored gain (KGyV) determined from speed (V) and lateral acceleration (Gy), a control command for controlling the longitudinal acceleration of the vehicle is generated on the basis of the multiplied value, and the generated control command is output. According to this method, as mentioned in NPL 1, a trajectory of the combined acceleration vector (G) of the longitudinal acceleration and the lateral acceleration is directed so as to draw a smooth curve (Vectoring) in the coordinate system with the fixed vehicle center of gravity, which is referred to as a G-Vectoring Control (GVC).